Position dependent damper for a vehicle suspension system

ABSTRACT

A damper assembly for a vehicle suspension system includes a primary damper and a secondary damper. The secondary damper includes a housing having a wall that at least partially surrounds at least a portion of the primary damper, the volume between the wall and the primary damper defining a chamber, and the wall defines an aperture. The secondary damper also includes a piston positioned within the chamber, a conduit defining a flow path that includes the aperture, and a valve disposed along the flow path. The secondary damper is configured to provide a damping force that varies based on the position of the piston within the chamber.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/048,931, filed Feb. 19, 2016, which is a continuation of U.S.application Ser. No. 14/334,305, filed Jul. 17, 2014, now U.S. Pat. No.9,291,230, which is a continuation of U.S. application Ser. No.13/792,154, filed Mar. 10, 2013, now U.S. Pat. No. 8,801,017, whichclaims the benefit of U.S. Provisional Patent Application No.61/615,717, filed Mar. 26, 2012, all of which are incorporated herein byreference in their entireties.

BACKGROUND

The present application relates generally to the field of suspensionsystems for vehicles. More specifically, the present application relatesto hydraulic dampers. Dampers (i.e. dashpots, hydraulic shock absorbers,etc.) dissipate kinetic energy as part of a vehicle suspension system.Dampers often include a housing, end caps, a piston, and a rod that iscoupled to the piston. Energy is dissipated through a hydraulic fluidflow along a hydraulic circuit (e.g., between a first chamber within thehousing to a second chamber within the housing). The piston includes aplurality of orifices that are covered with a shim stack (i.e. aplurality of compressed shims). As the piston moves through the housing,hydraulic fluid is forced from the first chamber, through the piston,and into the second chamber. Specifically, pressurized hydraulic fluidis forced through the orifices within the piston, deflects a portion ofthe shims to create an opening, and flows into the second chamber bypassing through the opening. Such traditional dampers provide a dampingforce that does not vary based on the location of the piston along thelength of the housing.

Traditional vehicle suspension systems incorporate/these dampers andother devices as part of a suspension damping strategy. By way ofexample, the vehicle suspension may also include a spring coupled inparallel with the damper to a swing arm. In jounce, the damper and thespring are compressed, and the damper imparts a resistive force. Such avehicle suspension strategy results in large total force that istransmitted to the occupants of the vehicle.

SUMMARY

One embodiment of the invention relates to a damper assembly for avehicle suspension system that includes a primary damper and a secondarydamper. The secondary damper includes a housing having a wall that atleast partially surrounds at least a portion of the primary damper, thevolume between the wall and the primary damper defining a chamber, andthe wall defines an aperture. The secondary damper also includes apiston positioned within the chamber, a conduit defining a flow paththat includes the aperture, and a valve disposed along the flow path.The secondary damper is configured to provide a damping force thatvaries based on the position of the piston within the chamber.

Another embodiment of the invention relates to a damper assembly for avehicle suspension system that includes a housing, a piston, a firstconduit, a second conduit, a first valve, and a second valve. Thehousing includes a wall that defines an inner volume, a first aperture,and a second aperture spaced from the first aperture along a length ofthe housing. The piston is disposed within the inner volume andconfigured to move between a first position and a second position. Thefirst conduit defines a first flow path that includes the firstaperture, and the second conduit defines a second flow path thatincludes the second aperture. The first valve is disposed along thefirst flow path and the second valve is disposed along the second flowpath. The first valve and the second valve are bidirectional flow valveshaving different damping characteristics, and at least one of the firstvalve and the second valve is configured to provide a first level ofdamping as the piston extends from the first position to the secondposition and a second level of damping as the piston retracts from thesecond position to the first position.

Still another embodiment of the invention relates to a suspension for avehicle that includes a wheel assembly, an interface configured toengage a chassis of the vehicle, and a damper assembly coupled to thewheel assembly and the interface. The damper assembly includes a primaryand a secondary damper. The secondary damper includes a housing, apiston, a conduit, and a valve. The housing includes a wall that atleast partially surrounds at least a portion of the primary damper, thevolume between the wall and the primary damper defining a chamber, andthe wall defines an aperture. The piston is positioned within thechamber, the conduit defines a flow path that includes the aperture, andthe valve is disposed along the flow path. The secondary damper isconfigured to provide a damping force that varies based on the positionof the piston within the chamber.

The invention is capable of other embodiments and of being carried outin various ways. Alternative exemplary embodiments relate to otherfeatures and combinations of features as may be recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is an elevation view of an axle assembly, according to anexemplary embodiment.

FIG. 2 is an elevation view of a suspension system, according to anexemplary embodiment.

FIGS. 3-4 are sectional views of an inner damper assembly, according toan exemplary embodiment.

FIGS. 5-6 are sectional views of an inner damper assembly, according toan exemplary embodiment.

FIG. 7 is a graphical representation of force versus spring deflectionfor a vehicle suspension system, according to an exemplary embodiment.

FIG. 8 is an elevation view of a coaxially integrated double damper,according to an exemplary embodiment.

FIGS. 9A-9C are partial sectional views of a coaxially integrated doubledamper, according to an exemplary embodiment.

FIG. 10 is a schematic view of an outer damper assembly having aplurality of hydraulic circuits, according to an exemplary embodiment.

FIGS. 11A-11F are schematic sectional views of an outer damper assemblyshowing varying piston locations, according to an exemplary embodiment.

FIG. 12 is a graphical representation of force versus velocity forvalves of an outer damper assembly, according to an exemplaryembodiment.

FIG. 13 is a graphical representation of force versus velocity andposition of an outer damper assembly, according to an exemplaryembodiment.

FIG. 14 is an elevation view of a coaxially integrated double damper,according to an exemplary embodiment.

FIGS. 15A-15C are sectional views of a coaxially integrated doubledamper, according to an exemplary embodiment.

FIG. 16 is a sectional view of an outer housing showing a plurality ofopenings and conduits, according to an exemplary embodiment.

FIGS. 17A-17B are elevation views of an outer damper assembly havingflow control valves, according to an exemplary embodiment.

FIG. 18 is a sectional view showing a plurality of conduits that couplethe openings within the outer housing, according to an exemplaryembodiment.

FIG. 19 is an elevation view of a vehicle suspension system havingcross-plumbed dampers, according to an exemplary embodiment.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the presentapplication is not limited to the details or methodology set forth inthe description or illustrated in the figures. It should also beunderstood that the terminology is for the purpose of description onlyand should not be regarded as limiting.

Referring to the exemplary embodiment shown in FIG. 1, an axle assembly110 is configured to be included as part of a vehicle. The vehicle maybe a military vehicle, a utility vehicle (e.g., a fire truck, a tractor,construction equipment, a sport utility vehicle, etc.), or still anothertype of vehicle. As shown in FIG. 1, axle assembly 110 includes adifferential 112 coupled to a half shaft 114. As shown in FIG. 1, halfshaft 114 is coupled to a wheel-end assembly 116. The wheel-end assembly116 may include brakes, a gear reduction, steering components, a wheelhub, a wheel, a tire, and other features. According to an exemplaryembodiment, the differential 112 is configured to be coupled to a driveshaft of the vehicle. Such a differential 112 may receive rotationalenergy from a prime mover (e.g., a diesel engine, a gasoline engine, anelectric motor, etc.) of the vehicle. The differential 112 thenallocates torque provided by the prime mover between the half shafts 114of the axle assembly 110. The half shafts 114 deliver the rotationalenergy to each wheel-end assembly 116. According to an alternativeembodiment, each wheel-end assembly 116 includes a prime mover (e.g.,the axle assembly 110 includes electric motors that each drive onewheel).

According to an exemplary embodiment, the axle assembly 110 includes asuspension system 118 that couples the chassis of the vehicle towheel-end assembly 116. In some embodiments, the chassis includes a pairof opposing frame rails, and the suspension system 118 engages theopposing frame rails through side plate assemblies. In otherembodiments, the chassis is a hull, a capsule, or another type ofstructural member. According to an exemplary embodiment, the suspensionsystem 118 includes a spring, shown as gas spring 120, and a damper,shown as hydraulic damper 122. As shown in FIG. 1, the gas spring 120and the hydraulic damper 122 are coupled in parallel to a lower supportmember, shown as lower swing arm 126. According to an exemplaryembodiment, the wheel-end assembly 116 is coupled to lower swing arm 126and an upper support member, shown as upper swing arm 124.

According to an exemplary embodiment, the vehicle is configured foroperation on both smooth (e.g., paved) and uneven (e.g., off-road,rough, etc.) terrain. As the vehicle travels over uneven terrain, theupper swing arm 124 and the lower swing arm 126 guide the verticalmovement of the wheel-end assembly 116. A stop, shown as cushion 128,provides an upper bound to the movement of the wheel-end assembly 116.It should be understood that axle assembly 110 may include similarcomponents (e.g., wheel end assemblies, suspension assemblies, swingarms, etc.) for each of the two opposing lateral sides of a vehicle.

Referring next to the exemplary embodiment shown in FIG. 2, thesuspension system 118 includes various components configured to improveperformance of the vehicle. As shown in FIG. 2, gas spring 120 is a highpressure gas spring. According to an exemplary embodiment, thesuspension system 118 includes a pump, shown as high-pressure gas pump130, that is coupled to gas spring 120. In some embodiments, suspensionsystem 118 includes a plurality of high-pressure gas pumps 130 eachcoupled to a separate gas spring 120. In other embodiments, thesuspension system 118 includes fewer high-pressure gas pumps 130 thangas springs 120. According to an exemplary embodiment, the gas springand the pump include gas made up of at least 90% inert gas (e.g.,nitrogen, argon, helium, etc.). The gas may be stored, provided, orreceived in one or more reservoirs (e.g., tank, accumulators, etc.).During operation, the high-pressure gas pump 130 selectively providesgas, under pressure, to at least one of the gas springs 120 and thereservoir. In some embodiments, at least one of the gas springs 120 andthe hydraulic dampers 122 receive and provide a fluid (e.g., gas,hydraulic fluid) to lift or lower the body of the vehicle with respectto the ground thereby changing the ride height of the vehicle.

Referring next to the exemplary embodiment shown in FIGS. 3-4, a damperincludes a base damper, shown as inner damper assembly 210. According toan exemplary embodiment, hydraulic damper 200 is included as part of asuspension system and an axle assembly. As shown in FIGS. 3-4, hydraulicdamper 200 includes a housing, shown as outer cylinder 212, and atubular element, shown as inner cylinder 214. According to an exemplaryembodiment, the inner cylinder 214 is disposed at least partially withinthe outer cylinder 212. A first end, shown as cap 216, is coupled to anend of both the inner cylinder 214 and the outer cylinder 212. A tubularelement, shown as plunger 218, is slidably coupled to the inner cylinder214 and received within the outer cylinder 212. A second end, shown ascap 224, couples outer cylinder 212 to plunger 218. A first chamber 220is defined by the an inner surface of the plunger 218, the cap 216, andan inner surface of the inner cylinder 214. According to an exemplaryembodiment, movement of the plunger 218 relative to the inner cylinder214 changes the volume of the first chamber 220. A second chamber 226 isdefined by cap 224, an inner surface of outer cylinder 212, and cap 216.

According to the exemplary embodiment shown in FIGS. 3-4, the innerdamper assembly 210 further includes a piston, shown as plunger 222,positioned within the second chamber 226. According to an exemplaryembodiment, plunger 222 is disk-shaped and defines a circular aperturethereby forming an annular ring. As shown in FIGS. 3-4, the plunger 222is coupled to plunger 218. The plunger 222 separates second chamber 226into a compression chamber 232 and an extension chamber 231. The secondchamber 226 is an annular chamber and may include one or moresub-chambers in fluid communication with one another

According to an exemplary embodiment, the cap 216 of inner damperassembly 210 defines a first aperture (i.e., opening, hole, conduit,etc.), shown as first aperture 228, and the cap 224 of defines a secondaperture, shown as second aperture 230. As shown in FIG. 3, firstaperture 228 is associated with the first chamber 220 and secondaperture 230 is associated with the second chamber 226. In someembodiments, the first aperture 228 is coupled to a transfer tube andallows a fluid (e.g., hydraulic fluid, oil, gas, etc.) to flow betweenthe first chamber 220 and other components. The second aperture may alsobe coupled to transfer tubes and allow a fluid to flow between secondchamber 226 and other components. Valves (e.g., directional-controlvalves, etc.) positioned along such transfer tubes (e.g., coupled to theinner damper assembly 210, remotely positioned but in fluidcommunication with first chamber 220 and second chamber 226, etc.) mayprovide damping forces. According to an alternative embodiment, theinner damper assembly 210 functions as a spring or an accumulator (i.e.first chamber 220 and second chamber 226 may be sealed).

As shown in FIGS. 3-4, the plunger 222 is coupled to the plunger 218such that the plunger 222 and the plunger 218 travel at the same rate.According to an exemplary embodiment, the plunger 218 may slide towardcap 216 thereby pushing fluid out of the first chamber 220. The plunger222 may also slide toward cap 216 at the same rate thereby drawing fluidinto the extension chamber 231 of second chamber 226. According to analternative embodiment, the plunger 222 is fixed to the inner cylinder214 and slides relative to both the plunger 218 and the outer cylinder212.

According to an exemplary embodiment, an end portion of the plunger 218(e.g., the portion that is orthogonal to a longitudinal axis of plunger218) has a cross-sectional area that is substantially equal (e.g.,within ten percent) to the portion of the plunger 222 that is exposed toextension chamber 231. The substantially equal cross-sectional areasprovide a one-to-one working area ratio. According to an exemplaryembodiment, the rate of volume change within the first chamber 220 isequal to the rate of volume change within the extension chamber 231(i.e. the rate that hydraulic fluid exits first chamber 220 andextension chamber 231 is equal to the rate that hydraulic fluid entersthe other of first chamber 220 and extension chamber 231).

According to an exemplary embodiment, inner damper assembly 210 operatesindependently (i.e. not cross-linked with other dampers). The firstaperture 228 may be coupled to the second aperture 230 such thathydraulic fluid from one of the first chamber 220 and the second chamber226 flows directly to the other of the first chamber 220 and the secondchamber 226. A damper that couples first aperture 228 and secondaperture 230 requires no make-up volume of hydraulic fluid and providesa simplified alternative to systems that utilize an intermediateaccumulator or a double rod-end cylinder configuration.

As shown in FIG. 4, the face of the plunger 222 that at least partiallydefines the compression chamber 232 has about a twenty-five percentlarger working area than the side of the plunger 222 that is defines theextension chamber 231. According to an alternative embodiment, theextension chamber 231 and the compression chamber 232 contain hydraulicfluid and the first chamber 220 forms a vacuum, contains an inert gas,or is in fluid communication with the environment. Such an inner damperassembly 210 may include a port allowing fluid flow from compressionchamber 232 thereby providing an extend-to-retract ratio of about1-to-1.25 (i.e. near equal area ratio).

Referring next to the alternative embodiment shown in FIGS. 5-6, aninner damper assembly, shown as inner damper assembly 300, includes afirst subassembly, shown as first damper assembly 310, and a secondsubassembly, shown as second damper assembly 330. As shown in FIG. 5-6,the first damper assembly 310 and the second damper assembly 330 arearranged coaxially to form inner damper assembly 300. According to anexemplary embodiment, inner damper assembly 300 is implemented as partof a vehicle suspension system. The first damper assembly 310 includes atubular member, shown as plunger 312, that defines an inner volume and apiston, shown as plunger 316, coupled to an end of the plunger 312. Atubular member, shown as inner cylinder 314, is slidably coupled toplunger 316. According to an exemplary embodiment, plunger 312 andplunger 316 are positioned at least partially within an inner volume ofinner cylinder 314. A cover, shown cap 318, is coupled to a first end ofinner cylinder 314. As shown in FIGS. 5-6, a cover, shown as cap 319, iscoupled to an end of plunger 312 and plunger 316. A first volume, shownas chamber 320, is defined by a face of plunger 316, an inner surface ofinner cylinder 314, and cap 318. A second volume, shown as chamber 322,is defined by an opposing face of plunger 316, an inner surface of innercylinder 314, an outer surface of plunger 312, and cap 319. Translationof the plunger 316 relative to inner cylinder 314 changes the volume ofchamber 320 and chamber 322.

According to an exemplary embodiment, the second damper assembly 330includes a piston, shown as plunger 332, that is fixed to an end of theinner cylinder 314 opposite cap 318. As shown in FIG. 6, the plunger 332moves with the inner cylinder 314. A tubular member, shown as cylinder334, and an external tubular member, shown as outer tubular member 336,each include a sidewall that defines an inner volume. As shown in FIGS.5-6, the first damper assembly 310 and the plunger 332 are positioned atleast partially within the inner volume of cylinder 334. Each of theinner damper, the plunger 332, and cylinder 334 are positioned withinthe inner volume of outer tubular member 336. As shown in FIGS. 5-6, anend, shown as cap 338 is coupled to an end of cylinder 334 and outertubular member 336. The cap 338, an inner surface of cylinder 334, andouter surface of inner cylinder 314, and a surface of plunger 332 definea volume, shown as chamber 340. According to an exemplary embodiment,the cross-sectional area of the portion of plunger 316 that partiallyforms chamber 320 is substantially equal to the cross-sectional area ofthe portion of plunger 332 that partially defines chamber 340 therebyproviding a one-to-one working area ratio.

The inner damper assembly 300 includes a first port 352 and a secondport 354 defined within an end assembly 350. As shown in FIGS. 5-6, theplunger 312 defines a first aperture, shown as conduit 360, extendingbetween first chamber 320 and first port 352. According to an exemplaryembodiment, chamber 340 is in fluid communication with second port 354through a flow path, shown as passage 362. As shown in FIGS. 5-6,passage 362 includes an aperture defined in a sidewall of cylinder 334,a volume between an outer surface of cylinder 334 and an inner surfaceof outer tubular member 336, and within a portion of the end assembly350. According to an exemplary embodiment, the first port 352 and secondport 354 are positioned along a common surface of end assembly 350. Amodular valve assembly, shown as valve assembly 370, is coupled to endassembly 350 and positioned over first port 352 and second port 354.

During a mode of operation of the inner damper assembly 300, thecomponents move relative to one another from the retracted positionshown in FIG. 5 to the extended position shown in FIG. 6. According toan exemplary embodiment, the inner cylinder 314 slides away from theplunger 316, and the volume of the first chamber 320 increases. Theplunger 332 slides toward the cap 338, decreasing the volume of thechamber 340. Fluid flows into the first port 352, through conduit 360 inthe plunger 312 and plunger 316, and into the first chamber 320. Fluidflows from the chamber 340, through the passage 362, and to the secondport 354. According to an exemplary embodiment, inner damper assembly300 is independent (i.e. not cross-linked), and first port 352 is influid communication with second port 354.

According to an exemplary embodiment, the vehicle suspension systemimplements a spring force compensation strategy that reduces the totalforce imparted onto occupants within the vehicle by a road surface. Itshould be understood that traditional dampers generate compressionforces in jounce and rebound (i.e. when the spring is compressed andextended). As shown in FIG. 7, the damper of the present applicationprovides recoil damping in jounce when the spring forces are greatestand compressive damping in rebound when the spring force is reduced.

As the wheel encounters a positive obstacle (e.g., a bump, a curb,etc.), the wheel end travels upward from an equilibrium point (e.g., theposition where the piston is located when the vehicle is traveling onflat ground) in a jounce motion. A jounce motion compresses the springand retracts the damper. Retraction of the damper generates compressiondamping forces. As the wheel passes over the positive obstacle or as thewheel encounters a negative obstacle (e.g., a depression, a void, etc.),the wheel end travels downward in a rebound motion. A rebound motionextends the spring and the damper thereby transferring energy from thecompressed spring into the suspension system and occupants of thevehicle. In a rebound motion, extension of the damper generates recoildamping.

According to the exemplary embodiment shown in FIG. 7, the damperproduces little compression damping (e.g., under five kilonewtons at aspeed of one meter per second) as the piston moves from an equilibriumpoint (e.g., where the spring deflection is about zero) toward thecompressed end of stroke (e.g., where the spring deflection is abouteight inches). In some instances, the forces imparted on the suspensionsystem are sufficient to compress the spring and damper to the end ofstroke. At the end of stroke, a portion of the suspension system (e.g.,the swing arm) may contact a hard stop (e.g., a polymeric cushion).After encountering the positive obstacle, the spring and the damperextend. According to an exemplary embodiment, the damper generatesgreater recoil damping forces during extension (e.g., thirty twokilonewtons at a speed of one meter per second). The damper alsodissipates energy stored in the compressed spring thereby reducing thelikelihood that the spring and damper will overshoot the equilibriumpoint. As shown in FIG. 7, the damper produces little recoil damping asthe piston moves from an equilibrium point toward the extended end ofstroke (e.g., where the spring deflection is about negative five inches.According to an exemplary embodiment, the damper provides compressiondamping as the spring and damper are retracted after encountering thenegative obstacle. This differs from conventional off-road suspensionsystems that add compression damping in the jounce position and allowextension to reposition the damper for another positive obstacle. Such aspring force compensation strategy is intended to separate recoildamping forces and compression damping forces thereby reducing the totalacceleration imparted to occupants of the vehicle at the peak of thepositive obstacle or lowest point of the negative obstacle. As a result,the vehicle's speed over off-road terrain can be improved for a fixedoccupant vibration level. Such a system reduces forces imparted tooccupants without the need for sensors, electronic controls, or othercomponents.

Referring next to the exemplary embodiment shown in FIGS. 8-9C, adamper, shown as damper assembly 400, includes a manifold 410 coupled toa body portion 420 with a rod 430. As shown in FIG. 8, manifold 410includes an interface, shown as joint 411, that is configured to engagea portion of the vehicle (e.g., the chassis, a hull, etc.). The bodyportion 420 defines an interface 422 that is configured to engage aportion of the vehicle (e.g., a lower swing arm, etc.). According to anexemplary embodiment, damper assembly 400 is a coaxially integrateddouble damper that facilitates the spring force compensation strategywhile providing damping forces that vary based on the position of thedamping piston.

As shown in FIGS. 9A-9C, damper assembly 400 includes a base damperassembly, shown as primary damper 440 (i.e. an inner damper assembly)and a supplemental damper, shown as secondary damper 460 (i.e. an outerdamper assembly). According to an exemplary embodiment, the primarydamper 440 provides roll control and base damping through an innerdamper circuit and the secondary damper 460 provides position dependentdamping through an outer damping circuit. The secondary damper 460provides damping forces that are independent of those provided byprimary damper 440. According to an exemplary embodiment, the dampingforces provided by secondary damper 460 are negligible in conditionswhere the primary damper 440 alone is designed to provide dampingforces. According to an exemplary embodiment, the primary damper 440 andthe secondary damper 460 are integrated into a single unit therebyreducing the size and weight of damper assembly 400. As shown in FIG.9A, the primary damper 440 and the secondary damper 460 are positionedcoaxially, which further reduces the size of primary damper 440 (e.g.,relative to two dampers positioned in series or parallel).

According to an exemplary embodiment, the primary damper 440 includes afirst tubular member 442 positioned within a second tubular member 444.As shown in FIG. 9A, a first piston, shown as plunger 446, is coupled toan end of first tubular member 442 and second tubular member 444. Theprimary damper 440 includes a third tubular member 448 at leastpartially surrounding the second tubular member 444. An aperture, shownas aperture 449, extends through a sidewall of the third tubular member448. According to an exemplary embodiment, plunger 446 is slidablycoupled to an inner surface of third tubular member 448. A first end cap450 and a second end cap 452 are coupled to opposing ends of thirdtubular member 448. As shown in FIG. 9A an outer surface of secondtubular member 444 is positioned within an aperture defined by secondend cap 452.

As shown in FIG. 9A, the secondary damper 460 includes a housing, shownas outer housing 470, a second piston, shown as plunger 462, and atubular member 464. According to an exemplary embodiment, outer housing470 defines a plurality of apertures, shown as openings 472. Accordingto an exemplary embodiment, conduits hydraulically couple a portion ofthe openings 472 to other openings 472 thereby forming at least onehydraulic circuit.

According to an exemplary embodiment, the tubular member 464 ispositioned coaxially with the first tubular member 442 and the secondtubular member 444. An end cap 466 is coupled to an end of outer housing470, and the tubular member 464 is slidably coupled between the secondend cap 452 and the end cap 466. According to an exemplary embodiment,plunger 462 has an annular shape that defines an aperture extendingtherethrough. The plunger 462 is disposed between an inner surface ofthe outer housing 470 and an outer surface of third tubular member 448.Referring again to the exemplary embodiment shown in FIG. 9A, anaperture, shown as aperture 445, extends through a sidewall of thesecond tubular member 444. It should be understood that the componentsof damper assembly 400 may have various cross-sectional shapes (e.g.,cylindrical, rectangular, square, hexagonal, etc.). According to anexemplary embodiment, the components of damper assembly 400 are coupledtogether with seals (e.g., bushings, o-rings, etc.) that are configuredto prevent pressurized fluid from passing between the chambers discussedherein or leaking out of damper assembly 400.

Referring again to FIGS. 9A-9C primary damper 440 and secondary damper460 define a plurality of flow channels. According to an exemplaryembodiment, primary damper 440 defines a compression chamber 480 that isformed by an inner surface of third tubular member 448, first end cap450, an end of first tubular member 442, and a first face of plunger446. A flow channel 482 is defined by an inner surface of first tubularmember 442 between the compression chamber 480, manifold 410, and afirst flow port 412. According to an exemplary embodiment, the primarydamper 440 includes an extension chamber 484 defined by an inner surfaceof tubular member 464, a second face of plunger 446, a portion ofplunger 462, and a face of second end cap 452. It should be understoodthat aperture 445 and aperture 449 facilitate the formation of extensionchamber 484 by placing various internal chambers in fluid communication.A flow channel 486 is defined by an inner surface of second tubularmember 444, an outer surface of first tubular member 442, manifold 410,and a second flow port 414. According to an exemplary embodiment, theflow channel 482 and the flow channel 486 form the inner damper circuit.An inner surface of the outer housing 470, first end cap 450, an outersurface of third tubular member 448, and a first surface of plunger 462define a secondary compression chamber 490, and the inner surface of theouter housing 470, end cap 466, an outer surface of tubular member 464,and a second surface of plunger 462 define a secondary extension chamber492.

Extension and retraction of the damper assembly 400 provides relativemovement between a first set of components (e.g., plunger 446, firsttubular member 442, second tubular member 444, tubular member 464, endcap 466, etc.) and a second set of components (e.g., outer housing 470,first end cap 450, third tubular member 448, second end cap 452, etc.).Such extension and retraction causes fluid to flow through the flowchannel 482 and flow channel 486 in opposite directions (e.g., fluidflows into compression chamber 480 and out of extension chamber 484 asthe damper assembly 400 is extended). According to an exemplaryembodiment, the area of plunger 446 and first tubular member 442 exposedto compression chamber 480 is approximately equal to the area of plunger446 and plunger 462 that are exposed to extension chamber 484 therebyproviding a one-to-one working area ratio.

Extension and retraction of the damper assembly 400 also providesrelative movement between plunger 462 and outer housing 470. Accordingto an exemplary embodiment, plunger 462 is coupled to plunger 446 (e.g.,with tubular member 464, manifold 410, and first tubular member 442). Asdamper assembly 400 is compressed, fluid is forced from secondarycompression chamber 490, through a first set of openings 472 to a secondset of openings 472 via a conduit, and into a secondary extensionchamber 492. As damper assembly 400 is extended, fluid is forced fromsecondary extension chamber 492, through a first set of openings 472 toa second set of openings 472 via a conduit, and into secondarycompression chamber 490. Fluid is forced through specific openings 472based on the position of plunger 462 within outer housing 470. Certainsets of openings may be deactivated (e.g., due to hydraulic lock,because a set of the openings is obstructed by plunger 462, etc.).

Referring next to the exemplary embodiment shown in FIG. 10, a schematicview of the outer damper circuits illustrates a configuration of asecondary damper 500. As shown in FIG. 10, the secondary damper 500includes a housing, shown as outer housing 510, that defines a pluralityof staggered openings 520 through a cylindrical sidewall. The staggeredopenings 520 may be positioned circumferentially offset from one anotherand located at various positions along the length of outer housing 510.

According to an exemplary embodiment, the plurality of staggeredopenings includes a first set having openings 522 and openings 523, asecond set having openings 524 and openings 525, a third set havingopenings 526 and openings 527, and a fourth set having openings 528 andopenings 529. Openings 522 are hydraulically coupled to openings 523with a first conduit 532, openings 524 are hydraulically coupled toopenings 525 with a second conduit 534, openings 526 are hydraulicallycoupled to openings 527 with a third conduit 536, and openings 528 arehydraulically coupled to openings 529 with a fourth conduit 538,according to an exemplary embodiment.

As shown in FIG. 10, a first valve 542, a second valve 544, a thirdvalve 546, and a fourth valve 548 are positioned along first conduit532, second conduit 534, third conduit 536, and fourth conduit 538,respectively. According to an exemplary embodiment, such valves arebi-directional flow valves configured to differentially restrict a fluidflow based on the direction that the fluid is flowing. A piston, shownas plunger 512, is coupled to outer housing 510 and separates an innervolume of outer housing 510 into a compression chamber 514 and anextension chamber 516. As shown in FIG. 10, a reservoir, shown asaccumulator 550, is coupled to first conduit 532. Accumulator 550 mayprovide a supplemental volume of fluid to, by way of example, reducecavitation and foaming of the fluid.

According to an exemplary embodiment, secondary damper 500 providesdamping forces that vary based on a position of plunger 512 along outerhousing 510. As the plunger 512 translates, a series of staggeredopenings 520 are activated or deactivated. The particular openings thatare activated and the number of openings that are activated bothcontribute to the damping forces provided by secondary damper 500,according to an exemplary embodiment. As shown in FIG. 10, the openingsare asymmetrically positioned along the length of outer housing 510,which contributes to the production of damping forces that are differentat each end of stroke. According to an exemplary embodiment, thesecondary damper 500 implements a spring force compensation dampingstrategy and provides damping that varies based on the position of theplunger 512 and the direction that the plunger 512 is traveling.Specifically, recoil damping is added when the spring force is high(e.g., in the jounce position), and compression damping is added whenthe spring force is low (e.g., in the rebound position).

Referring next to FIGS. 11A-11F, plunger 512 is shown as translatingalong outer housing 510 from an extended position to a retractedposition (e.g., after the vehicle encountered a negative obstacle). Thestaggered openings 520 may be hydraulically coupled, as shown in FIG.10. Fluid flows through certain staggered openings 520 based on theposition of plunger 512, thereby creating seven position dependentdamping zones. As shown in FIG. 11A, plunger 512 is initially positionedat full extension and translates in initial compression along directionof travel 518. Based on the position and travel direction of plunger512, fluid flows from openings 526 and openings 528 to openings 527 andopenings 529, respectively (e.g., due to a pressure differential betweenthe fluid at openings 526 and openings 527). The flow paths fromopenings 522 to openings 523 and openings 524 to openings 525 aredeactivated due to hydraulic lock (i.e. pressurized fluid is exposed toboth sides of each hydraulic circuit thereby preventing fluid fromflowing between the openings).

As shown in FIG. 11B, the plunger 512 translated along direction oftravel 518. In such a position, the flow path between openings 522 andopenings 523 is deactivated (e.g., because plunger 512 is blockingopenings 523), and fluid flow occurs from openings 524 to openings 525,openings 526 to openings 527, and openings 528 to openings 529. As shownin FIG. 11C, plunger 512 has traveled beyond openings 523 and fluid flowoccurs from openings 522 to openings 523, openings 524 to openings 525,openings 526 to openings 527, and openings 528 to openings 529.According to an exemplary embodiment, minimal fluid restriction occurswhen plunger 512 is positioned between openings 523 and openings 528such that the secondary damper produces a lowest level of dampingforces.

Referring next to FIG. 11D, plunger 512 compressed beyond a mid-range ofstroke, and fluid flow occurs from openings 522 to openings 523,openings 524 to openings 525, and from openings 526 to openings 527. Theflow path from openings 528 to openings 529 is deactivated due tohydraulic lock. As shown in FIG. 11E, flow occurs from openings 522 toopenings 523 and openings 524 to openings 525. The flow paths fromopenings 526 to openings 527 and openings 528 to openings 529 aredeactivated due to hydraulic lock. Referring finally to FIG. 11F,plunger 512 is nearing a compression end of stroke, and fluid flowoccurs only from openings 522 to openings 523. The flow paths from 524to openings 525, openings 526 to openings 527, and openings 528 toopenings 529 are deactivated due to hydraulic lock.

Referring again to FIG. 10, fluid flowing between the openings along theconduits interacts with valves. According to an exemplary embodiment,valve 546 and valve 548 have greater damping coefficients (i.e. flow ismore restricted) as the fluid flows from openings 526 to openings 527and from openings 528 to openings 529 (e.g., as illustrated in FIGS.11A-11C) than when fluid flows from openings 527 to openings 526 andopenings 529 to openings 528 (e.g., as plunger 512 moves in a directionopposite direction of travel 518). Such a valve 546 and valve 548facilitate damping that varies with the direction that plunger 512 istraveling. According to an exemplary embodiment, FIGS. 11A-11Cillustrate initial compression after a wheel end encounters a negativeobstacle, and valve 546 and valve 548 provide compression damping aspart of a spring force compensation strategy. The valve 546 and thevalve 548 do not restrict flow to the same extent, thereby providinglower damping forces, as plunger 512 travels along direction of travel518 and fluid flow occurs from openings 526 to openings 527 and openings528 to openings 529.

According to an exemplary embodiment, valve 542 and valve 544 have afirst level of damping coefficients (e.g., to produce a low level ofdamping) as fluid flow occurs from openings 522 to openings 523 andopenings 524 to openings 525. Such a flow path occurs as plunger 512approaches a compression end of stroke, as shown in FIGS. 11D-11F.According to an exemplary embodiment, valve 542 and valve 544 have agreater level of damping coefficients (e.g., to produce a large level ofdamping) as fluid flow occurs from openings 523 to openings 522 andopenings 525 to openings 524. Such flow may occur as plunger 512 movesin a direction opposite direction of travel 518 from the position shownin FIG. 11F. According to an exemplary embodiment, valve 542 and valve544 provide recoil damping as part of a spring force compensationstrategy. The number of flow paths that are activated and thecharacteristics of the valves along the activated flow paths contributeto the damping forces that the secondary damper 500 provides.

Referring next to FIG. 12, a graphical representation of force versusvelocity is shown for the various valves of the secondary damper.According to an exemplary embodiment, valve 542 is designed to provide alarge damping force for positive flow velocity (e.g., fluid flow fromopenings 523 to openings 522) and a small damping force for negativeflow velocity (e.g., fluid flow from openings 522 to openings 523). Asshown in FIG. 12, valve 544 also provides a large damping force forpositive flow velocity and a small damping force for negative flowvelocity. A spring force compensation strategy may impart large recoildamping during compression of the secondary damper with valve 542 andvalve 544 without providing large compression damping (e.g., due to thesmall damping force generated by valve 542 and valve 544 for flow fromopenings 522 and openings 524 to openings 523 and openings 525).According to an exemplary embodiment, valve 548 produces larger dampingforces for flow from openings 528 to openings 529 than for flow fromopenings 529 to openings 528. The openings 527 and the openings 529 arepositioned such that flow occurs concurrently through valve 546 andvalve 548 (i.e. valve 546 and valve 548 provide supplemental dampingforces). According to an exemplary embodiment, valve 546 and valve 548provide large compression damping during extension of the secondarydamper without providing large recoil damping as the spring is extended.

Referring next to FIG. 13, a three-dimensional representation of dampingforce as a function of velocity and displacement (i.e. stroke) of thepiston within the secondary damper is shown, according to an exemplaryembodiment. As shown in FIG. 13, the secondary damper provides dampingforces that vary based on the position of the piston. The damping forcesalso vary based on the direction that the piston is traveling (e.g., apositive velocity, a negative velocity, etc.). According to an exemplaryembodiment, the secondary damper provides large damping forces (e.g., 15kilonewtons) in rebound velocity at maximum bump travel (i.e. initialcompression from maximum extension).

Referring next to the exemplary embodiment shown in FIGS. 14-18, adamper assembly, shown as coaxial double damper assembly 600, includes amanifold 610, a rod portion 620, and a body portion 630. According to anexemplary embodiment, coaxial double damper assembly 600 providesdamping forces as rod portion 620 extends and retracts relative to bodyportion 630. As shown in FIGS. 15A-15C, coaxial double damper assembly600 includes a base damper assembly (i.e. an inner damper assembly),shown as primary damper 640, and a supplemental damper, shown assecondary damper 660. According to an exemplary embodiment, the primarydamper 640 provides roll control and base damping through an innerdamper circuit and the secondary damper 660 provides position dependentdamping through an outer damping circuit. The secondary damper 660provides damping forces that are independent of those provided byprimary damper 640. According to an exemplary embodiment, the dampingforces provided by secondary damper 660 are negligible in conditionswhere the primary damper 640 alone is designed to provide dampingforces. According to an exemplary embodiment, the primary damper 640 andthe secondary damper 660 are integrated into a single unit therebyreducing the size and weight of the coaxial double damper assembly 600.As shown in FIG. 15A, the primary damper 640 and the secondary damper660 are positioned coaxially, which further reduces the size of damperassembly 440 (e.g., relative to two dampers positioned in parallel).

According to an exemplary embodiment, the primary damper 640 includes afirst tubular member 642 positioned within a second tubular member 644.As shown in FIG. 15A, a first piston, shown as plunger 646, is coupledto an end of first tubular member 642 and second tubular member 644. Theprimary damper 640 includes a third tubular member 648 at leastpartially surrounding the second tubular member 644. An aperture, shownas aperture 649, extends through a sidewall of the third tubular member648. According to an exemplary embodiment, plunger 646 is slidablycoupled to an inner surface of third tubular member 648. A first end cap650 and a second end cap 652 are coupled to opposing ends of thirdtubular member 648. As shown in FIG. 15A, an outer surface of secondtubular member 644 is positioned within an aperture defined by secondend cap 652.

As shown in FIG. 15A, the secondary damper 660 includes a housing, shownas outer housing 670, a second piston, shown as plunger 662, and atubular member 664. According to an exemplary embodiment, outer housing670 defines a plurality of apertures, shown as openings 672. Accordingto an exemplary embodiment, conduits hydraulically couple a portion ofthe openings 672 to other openings 672 thereby forming at least onehydraulic circuit.

According to an exemplary embodiment, the tubular member 664 ispositioned coaxially with the first tubular member 642 and the secondtubular member 644. An end cap 666 is coupled to an end of outer housing670, and the tubular member 664 is slidably coupled between the secondend cap 652 and the end cap 666. According to an exemplary embodiment,plunger 662 has an annular shape that defines an aperture extendingtherethrough. The plunger 662 is disposed between an inner surface ofthe outer housing 670 and an outer surface of third tubular member 648.Referring again to the exemplary embodiment shown in FIGS. 15A-15C, anaperture, shown as aperture 645, extends through a sidewall of thesecond tubular member 644. It should be understood that the componentsof coaxial double damper assembly 600 may have various cross-sectionalshapes (e.g., cylindrical, rectangular, square, hexagonal, etc.).According to an exemplary embodiment, the components of coaxial doubledamper assembly 600 are coupled together with seals (e.g., bushings,o-rings, etc.) that are configured to prevent pressurized fluid frompassing between the chambers discussed herein or leaking out of coaxialdouble damper assembly 600.

Referring next to FIG. 16, outer housing 670 defines a plurality ofopenings 672. According to an exemplary embodiment, openings 672 areoffset relative to one another both circumferentially and along thelength of outer housing 670. As shown in FIG. 16, the plurality ofopenings 672 includes a first set having openings 682 and openings 683that are coupled with a conduit 692, a second set having openings 684and openings 685 that are coupled with a conduit 694, a third set havingopenings 686 and openings 687 that are coupled with a conduit 696, and afourth set having openings 688 and openings 689 that are coupled with aconduit 698. It should be understood that an accumulator may be coupledto at least one of conduit 692, conduit 694, conduit 696, and conduit698. As plunger 662 translates within outer housing 670 (e.g., due torelative movement between components of a vehicle suspension system)various openings and their corresponding conduits are activated anddeactivated. According to an exemplary embodiment, fluid flows throughthe activated openings and their corresponding conduits to providedamping forces that vary based on position and direction of the plunger662.

Referring next to FIGS. 17A-17B, a plurality of valves are positionedalong the conduits. As shown in FIG. 17B, a valve 712 is positionedalong conduit 692, a valve 714 is positioned along conduit 694, a valve716 is positioned along conduit 696, and a valve 718 is positioned alongconduit 698. In the embodiment shown in FIGS. 17A-17B, valve 712, valve714, valve 716, and valve 718 are coupled to outer housing 670.According to an alternative embodiment, valve 712, valve 714, valve 716,and valve 718 are coupled to another portion of body portion 630 orcoupled to a common manifold block. According to an exemplaryembodiment, valve 712, valve 714, valve 716, and valve 718 arebidirectional flow valves that differentially restrict a fluid flowbased on the direction that the fluid is flowing. Coaxial double damperassembly 600 may provide different damping forces for extension andretraction and different damping forces based on the position of thepiston. According to an exemplary embodiment, coaxial double damperassembly 600 provides recoil damping forces in jounce and compressiondamping forces in recoil as part of a spring force compensationstrategy.

According to the exemplary embodiment shown in FIG. 18, body portion 630includes outer housing 670, a first cover, shown as drilling member 674,and a second cover, shown as drilling member 676. According to anexemplary embodiment, drilling member 674 and drilling member 676 areremovably coupled to outer housing 670 with a plurality of fasteners(e.g., bolts, screws, etc.). According to an alternative embodiment,drilling member 674 and drilling member 676 are integrally formed withouter housing 670. As shown in the sectional view of FIG. 18, drillingmember 676 includes a plurality of drillings that form conduit 694 andconduit 696. According to an alternative embodiment, conduit 694 andconduit 696 are formed with tubular members coupled to an outer portionof outer housing 670 or with flow passages formed within outer housing670.

According to an exemplary embodiment, each damper assembly functionsindependently. Such damper assemblies may include a conduit coupling thechambers on opposing sides of a damping piston (e.g., the compressionchamber may be coupled to an extension chamber) to provide a flow pathfor the compressed fluid. An intermediate accumulator may be positionedbetween the chambers to reduce the temperature and prolong the life ofthe fluid. According to the exemplary embodiment shown in FIG. 19, asuspension system 800 includes dampers positioned on opposing lateralsides of the vehicle are cross-plumbed in a walking beam configurationthereby providing anti-roll functionality. As shown in FIG. 19, thesuspension system 800 includes a first damper 810 and a second damper820. First damper 810 and second damper 820 each include a manifoldblock, shown as manifold 812 and manifold 822, respectively. As shown inFIG. 19, a first hose 832 and a second hose 834 couple manifold 812 tomanifold 822. According to an exemplary embodiment, retraction of firstdamper 810 (e.g., due to a corresponding wheel end impacting a positiveobstacle) increases the pressure of a fluid within a compression chamber(e.g., a chamber positioned between a piston and a lower end cap offirst damper 810). The pressurized fluid flows through hose 834, whichis in fluid communication with an extension chamber (e.g., a chamberpositioned between a piston and manifold 822) of first damper 810.According to an exemplary embodiment, the cross-plumbed arrangementshown in FIG. 19 improves roll stiffness for a vehicle.

The construction and arrangements of the damper, as shown in the variousexemplary embodiments, are illustrative only. Although only a fewembodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Someelements shown as integrally formed may be constructed of multiple partsor elements, the position of elements may be reversed or otherwisevaried, and the nature or number of discrete elements or positions maybe altered or varied. The order or sequence of any process, logicalalgorithm, or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes andomissions may also be made in the design, operating conditions andarrangement of the various exemplary embodiments without departing fromthe scope of the present invention.

What is claimed is:
 1. A damper assembly for a vehicle suspensionsystem, comprising: a primary damper; and a secondary damper,comprising: a housing including a wall that at least partially surroundsat least a portion of the primary damper, the volume between the walland the primary damper defining a chamber, wherein the wall defines anaperture; a piston positioned within the chamber; a conduit defining aflow path that includes the aperture; and a valve disposed along theflow path, wherein the secondary damper is configured to provide adamping force that varies based on the position of the piston within thechamber.
 2. The damper assembly of claim 1, wherein the wall defines aset of apertures, the conduit defining the flow path between the set ofapertures.
 3. The damper assembly of claim 2, wherein the valvecomprises a bidirectional flow valve configured to produce differentdamping forces based on the position and the travel direction of thepiston.
 4. The damper assembly of claim 2, wherein the wall defines asecond set of apertures.
 5. The damper assembly of claim 4, furthercomprising a second conduit forming a second flow path between thesecond set of apertures, wherein the piston is configured such thatmovement thereof along the housing activates and deactivates the firstflow path and the second flow path.
 6. The damper assembly of claim 5,further comprising a second valve disposed along the second flow path.7. The damper assembly of claim 6, wherein the first valve and thesecond valve are bidirectional flow valves configured to producedifferent damping forces based on the position and the travel directionof the piston.
 8. The damper assembly of claim 7, wherein the firstvalve is configured to produce recoil damping forces when the secondarydamper is in a retracted position and the second valve is configured toproduce compression damping forces when the secondary damper is in anextended position.
 9. The damper assembly of claim 8, wherein theprimary damper and the secondary damper share a common central axisthereby forming a coaxial double damper.
 10. The damper assembly ofclaim 2, wherein the primary damper comprises: a housing including awall that defines an inner volume; a cap coupled to an end of thehousing; a piston slidably coupled to the wall and disposed within theinner volume; a first tubular rod extending through the cap and coupledto the piston; and a tubular member partially surrounding the firsttubular rod and coupled to the piston.
 11. The damper assembly of claim10, wherein the piston of the secondary damper is moveably coupled tothe piston of the primary damper.
 12. The damper assembly of claim 11,wherein the piston of the primary damper and the piston of the secondarydamper share a common central axis thereby forming a coaxial doubledamper.
 13. A damper assembly for a vehicle suspension system,comprising: a housing including a wall that defines an inner volume, afirst aperture, and a second aperture spaced from the first aperturealong a length of the housing; a piston disposed within the inner volumeand configured to move between a first position and a second position; afirst conduit defining a first flow path that includes the firstaperture; a second conduit defining a second flow path that includes thesecond aperture; and a first valve disposed along the first flow pathand a second valve disposed along the second flow path, wherein thefirst valve and the second valve are bidirectional flow valves havingdifferent damping characteristics, at least one of the first valve andthe second valve configured to provide a first level of damping as thepiston extends from the first position to the second position and asecond level of damping as the piston retracts from the second positionto the first position.
 14. The damper assembly of claim 13, wherein thewall of the housing defines a first set of apertures including the firstaperture, and wherein the wall of the housing defines a second set ofapertures including the second aperture.
 15. The damper assembly ofclaim 14, wherein the first conduit extends between the first set ofapertures, and wherein the second conduit extends between the second setof apertures.
 16. A suspension for a vehicle, comprising: a wheelassembly; an interface configured to engage a chassis of the vehicle;and a damper assembly coupled to the wheel assembly and the interface,comprising: a primary damper; and a secondary damper, comprising: ahousing including a wall that at least partially surrounds at least aportion of the primary damper, the volume between the wall and theprimary damper defining a chamber, wherein the wall defines an aperture;a piston positioned within the chamber; a conduit defining a flow paththat includes the aperture; and a valve disposed along the flow path,wherein the secondary damper is configured to provide a damping forcethat varies based on the position of the piston within the chamber. 17.The suspension of claim 16, wherein the primary damper and the secondarydamper share a common central axis thereby forming a coaxial doubledamper.
 18. The suspension of claim 17, wherein the secondary damper isconfigured to produce recoil damping forces when the piston is in aretracted position and is configured to produce compression dampingforces when the piston is in an extended position.
 19. The suspension ofclaim 18, wherein the piston of the secondary damper separates thechamber into a first volume and a second volume.
 20. The suspension ofclaim 19, further comprising a second damper assembly including ahousing defining a second chamber and a piston separating the secondchamber into a first volume and a second volume, wherein the firstvolume of the first damper assembly is coupled to the second volume ofthe second damper assembly in a cross-plumbed walking beam arrangement.